# Why does my car shake at idle? **Verdict:** Drive to a shop this week - **Most common cause:** Misfire from worn spark plugs or a weak ignition coil - **Urgency:** This week - **Typical fix:** $75-$900 - **Causes to check:** 5 ## Quick answer A car that shakes while stopped with the engine running most often has a misfire from worn spark plugs or a failing ignition coil, or worn engine mounts that pass normal engine vibration into the cabin. Vacuum leaks and a dirty throttle body are next. A flashing check engine light means a severe misfire, so limit driving. ## What is happening? At idle the engine turns only about 600 to 900 times a minute and makes very little power, so any unevenness is easy to feel. If one cylinder misfires, the crankshaft gets a gap in its push every revolution, which you feel as a steady shudder. If too much or too little air gets in, the RPM sags or hunts. And if the engine mounts are worn, even a healthy engine's normal vibration reaches the cabin. It matters because the two most common causes do different kinds of harm. A misfire sends unburned fuel into the exhaust, which can overheat and ruin the catalytic converter, a far bigger bill than plugs or a coil. A broken mount lets the engine move more than it should, stressing hoses, wiring, axles and the exhaust. Knowing whether the shake changes between Park and Drive is the quickest way to tell which one you have. ## What causes it? The 5 most likely reasons 1. **Misfire from worn spark plugs or a weak ignition coil** (most common), $150-$600. When one cylinder fires weakly or not at all, the crankshaft gets an uneven push on every turn and the whole car shakes in a steady rhythm. It shows up most at idle because the engine is turning slowly. It is typical on engines past their plug interval, and a cracked coil boot can misfire more in damp weather. How to confirm: The check engine light is on or flashing, and a code reader shows P0300 or a cylinder code from P0301 to P0308. The shake usually feels like a steady stumble rather than a buzz. Fix: Replace spark plugs and the failed coil. 2. **Worn or broken engine mounts** (common), $200-$800. Rubber or fluid-filled mounts hold the engine and soak up its vibration. As they crack, collapse or leak with age and heat, normal idle vibration comes straight through the steering wheel, seat and floor. The engine itself may run perfectly. It is most noticeable in Drive with your foot on the brake, because the engine twists against the mounts. How to confirm: The shake is much worse in Drive or Reverse than in Park or Neutral, and there are no codes. A helper may see the engine rock or hear a clunk as you shift into gear. Fix: Replace the worn engine or transmission mounts. 3. **Vacuum leak** (common), $100-$500. A cracked vacuum hose, split intake boot, leaking PCV hose or failed intake gasket lets in air the engine computer did not measure. At idle that extra air is a large share of the total, so the mixture runs lean and the engine shakes or hunts. Rubber hoses harden and crack with age, so leaks are common on older engines. How to confirm: You hear a hiss from the engine bay, and a scan shows P0171 or P0174 with high long-term fuel trims. The shake often smooths out when you raise the RPM. Fix: Replace the cracked hose, boot or gasket. 4. **Dirty throttle body or sticking idle air control** (less common), $75-$300. Carbon builds up around the throttle plate and narrows the small gap the engine breathes through at idle. RPM then sags below normal, and a low, lugging idle shakes the car, especially with the AC or headlights adding load. Engines used for short trips build carbon faster. Older cars may have a separate idle air control valve that sticks. How to confirm: Idle speed on the tachometer drops or surges when the AC turns on, and codes such as P0505, P0506 or P0507 may be stored. Black carbon is visible around the throttle plate. Fix: Clean the throttle body and relearn idle. 5. **Clogged or leaking fuel injector** (less common), $200-$900. An injector that is partly blocked by deposits, or one that sprays poorly, starves one cylinder of fuel. That cylinder makes less power, so the idle feels uneven even with a good spark. It is more likely on high-mileage engines, direct-injection engines and cars that sit for long periods. A leaking injector can also cause a fuel smell. How to confirm: A misfire code stays on the same cylinder after you swap that coil to another cylinder. A shop can confirm with an injector balance test or by checking its electrical pulse. Fix: Clean or replace the injector. ## How to narrow it down at home 1. Read the codes with an OBD-II scanner, or ask a parts store to read them free. Misfire, lean or idle codes point to the engine; no codes point toward the mounts. 2. Hold the brake and compare the shake in Park, Neutral and Drive. Much worse in Drive or Reverse is a classic engine mount sign. 3. With the engine idling and the hood up, listen for hissing and look for cracked or loose rubber hoses and a split intake boot. ## Is it safe to drive? > **Drive to a shop this week.** A mild shake at idle is usually safe to drive for a few days while you book a repair. If the check engine light is flashing, drive gently to a shop and avoid hard acceleration; if the engine clunks loudly or jumps when you shift, stop driving because a broken mount can let it shift. ## When does it become urgent? - The check engine light starts flashing: limit driving and get the car to a shop gently. - The engine stalls at stops or when the AC turns on. - You hear a loud clunk or see the engine jump when shifting into Drive or Reverse. - You smell raw fuel or rotten eggs, or see black smoke from the tailpipe. - The shake now continues while driving or the car loses power on hills. ## What will the repair cost? | Cause | Fix | Typical cost | | --- | --- | --- | | Misfire from worn spark plugs or a weak ignition coil | Replace spark plugs and the failed coil | $150-$600 | | Worn or broken engine mounts | Replace the worn engine or transmission mounts | $200-$800 | | Vacuum leak | Replace the cracked hose, boot or gasket | $100-$500 | | Dirty throttle body or sticking idle air control | Clean the throttle body and relearn idle | $75-$300 | | Clogged or leaking fuel injector | Clean or replace the injector | $200-$900 | Detailed breakdowns: [spark plug replacement cost](/cost/spark-plug-replacement), [ignition coil replacement cost](/cost/ignition-coil-replacement), [fuel injector replacement cost](/cost/fuel-injector-replacement). ## What to tell your mechanic Tell the shop whether the shake changes between Park and Drive, whether it is worse cold or hot or with the AC on, whether the check engine light was on or flashing, and when the plugs were last changed. They will read codes and misfire counts, check fuel trims for a vacuum leak, inspect plugs and coils, and check the mounts with the engine under load. ## How to prevent it - Replace spark plugs at the interval in your owner's manual, often 60,000 to 100,000 miles. - Have a check engine light read promptly so a small misfire is fixed before it harms the converter. - Clean the throttle body when idle starts to sag, using a cleaner safe for your throttle type. - Ask the shop to inspect engine mounts during oil changes on cars past about 80,000 miles. - Use the fuel grade your manual lists, from a busy station, to limit injector deposits. ## Which models get the most engine complaints? | Model | Engine complaints to NHTSA | All complaints | | --- | --- | --- | | [Ford Escape](/vehicles/ford-escape) | 3,905 | 10,274 | | [Chevrolet Silverado](/vehicles/chevrolet-silverado) | 2,167 | 7,658 | | [Kia Soul](/vehicles/kia-soul) | 2,079 | 3,189 | | [Hyundai Sonata](/vehicles/hyundai-sonata) | 2,059 | 4,126 | | [Honda Pilot](/vehicles/honda-pilot) | 1,989 | 5,776 | | [Ford Edge](/vehicles/ford-edge) | 1,944 | 5,306 | | [Hyundai Tucson](/vehicles/hyundai-tucson) | 1,932 | 5,363 | | [Kia Sorento](/vehicles/kia-sorento) | 1,899 | 4,128 | | [GMC Sierra](/vehicles/gmc-sierra) | 1,872 | 5,041 | | [Hyundai Santa Fe](/vehicles/hyundai-santa-fe) | 1,828 | 3,779 | Owner complaints filed with NHTSA in the engine category for 2015-2026 models of 63 popular cars. Counts follow sales as well as reliability, so compare each with the model's total. ## Trouble codes that often go with it - [P0300](/codes/p0300): Random/Multiple Cylinder Misfire Detected - [P0301](/codes/p0301): Cylinder 1 Misfire Detected - [P0302](/codes/p0302): Cylinder 2 Misfire Detected - [P0303](/codes/p0303): Cylinder 3 Misfire Detected - [P0304](/codes/p0304): Cylinder 4 Misfire Detected - [P0171](/codes/p0171): System Too Lean (Bank 1) - [P0174](/codes/p0174): System Too Lean (Bank 2) - [P0505](/codes/p0505): Idle Air Control System - [P0506](/codes/p0506): Idle Air Control System RPM Lower Than Expected - [P0507](/codes/p0507): Idle Air Control System RPM Higher Than Expected ## Frequently asked questions ### Why does my car shake at idle but smooth out when driving? Because a misfire, vacuum leak or worn mount is easiest to feel at low RPM, when the engine makes little power and runs slowly. At higher RPM the pulses blend together and the extra air from a leak matters less. The fault is still there, so it is worth checking. ### Can bad motor mounts cause shaking at idle? Yes, and it is one of the most common causes when there are no warning lights. Worn mounts stop absorbing normal engine vibration, so you feel it in the wheel and seat. The shake is usually much worse in Drive with your foot on the brake than in Park or Neutral. ### Is it safe to drive if my car shakes at idle? Usually yes for a short time, as long as the check engine light is not flashing and the car accelerates normally. A flashing light means a severe misfire that can damage the catalytic converter, so drive gently to a shop. A loud clunk when shifting can mean a broken mount. ### How much does it cost to fix a car that shakes at idle? It depends on the cause. Spark plugs and a coil run about 150 to 600 dollars, a vacuum leak 100 to 500, throttle body cleaning 75 to 300, and engine mounts about 200 to 800 dollars at an independent shop in 2026. A diagnosis first avoids paying for the wrong part. ### Why does my car shake at idle with the AC on? The AC compressor adds load, which pulls idle speed down and makes the engine work harder against its mounts. A dirty throttle body or weak idle control cannot add enough air, so the idle sags and shakes. Worn mounts and a failing compressor clutch can also make it worse with the AC running. ### Why does my car shake at a red light in Drive? In Drive the transmission is trying to move the car, so the engine twists against its mounts. Worn mounts let that twist and vibration through to the cabin. A low idle speed or a mild misfire makes it worse. If the shake fades in Neutral, the mounts are the prime suspect. ### Can low oil cause a car to shake at idle? Not usually directly, but very low oil can upset variable valve timing on many engines, which can make the idle rough and set timing codes. It can also cause noise and wear. Check the dipstick on level ground with the engine off, and top up to the full mark if it is low. ### Can a bad battery or alternator make a car shake at idle? Rarely. A weak alternator can put extra drag on the engine or let voltage drop, which may make idle uneven on some cars, and a disconnected battery can erase the learned idle. Plugs, coils, vacuum leaks and mounts are far more likely. A free charging test at a parts store rules it out. ### Can I fix shaking at idle myself? Often, yes. Reading codes, replacing spark plugs, swapping a suspect coil to another cylinder, cleaning the throttle body and replacing a cracked vacuum hose are common DIY jobs with basic tools. Engine mounts can be harder, since the engine must be supported safely while a mount is removed. ### Why does my car shake at idle when cold but not when warm? A cold engine runs richer and needs a strong spark, so a worn plug or weak coil may misfire until things warm up. A vacuum hose can leak when cold and seal as it expands. Cold rubber mounts are also stiffer. A shake that lasts more than a minute or two is worth checking. ## Sources - [EPA: On-Board Diagnostics (OBD)](https://www.epa.gov/state-and-local-transportation/vehicle-emissions-board-diagnostics-obd) - [Car Care Council: Car care guide](https://www.carcare.org/car-care-guide/) - [AAA: Approved Auto Repair](https://www.aaa.com/autorepair/) ## Other car problems - [Why is blue smoke coming from my exhaust?](https://diagxcar.com/symptoms/blue-smoke-from-exhaust) - [Why does my car smell like something is burning?](https://diagxcar.com/symptoms/burning-smell-from-car) - [Why does my car crank but not start?](https://diagxcar.com/symptoms/car-cranks-but-wont-start) - [Why does my car hesitate when I accelerate?](https://diagxcar.com/symptoms/car-hesitates-when-accelerating) - [Why does my car jerk when I accelerate?](https://diagxcar.com/symptoms/car-jerks-when-accelerating) - [Why is my car leaking oil?](https://diagxcar.com/symptoms/car-leaking-oil) - [Why does my car lose power when accelerating?](https://diagxcar.com/symptoms/car-loses-power-when-accelerating) - [Why does my car shake when I accelerate?](https://diagxcar.com/symptoms/car-shakes-when-accelerating) - [Why does my car pull to one side?](https://diagxcar.com/symptoms/car-pulls-to-one-side) - [Why does my car shake when I brake?](https://diagxcar.com/symptoms/car-shakes-when-braking) ## Repair costs - [Spark plug replacement cost](https://diagxcar.com/cost/spark-plug-replacement): $120-$450 - [Ignition coil replacement cost](https://diagxcar.com/cost/ignition-coil-replacement): $150-$400 - [Fuel injector replacement cost](https://diagxcar.com/cost/fuel-injector-replacement): $300-$1,500 ## How long parts last - [How often should you change your spark plugs?](https://diagxcar.com/how-often/change-spark-plugs): 30,000-100,000 miles ## Trouble codes that lead here - [P0015 "B" Camshaft Position - Timing Over-Retarded (Bank 1)](https://diagxcar.com/codes/p0015) - [P0019 Crankshaft Position - Camshaft Position Correlation (Bank 2 Sensor B)](https://diagxcar.com/codes/p0019) - [P0201 Injector Circuit/Open - Cylinder 1](https://diagxcar.com/codes/p0201) - [P0307 Cylinder 7 Misfire Detected](https://diagxcar.com/codes/p0307) - [P0308 Cylinder 8 Misfire Detected](https://diagxcar.com/codes/p0308) - [P0316 Engine Misfire Detected on Startup (First 1000 Revolutions)](https://diagxcar.com/codes/p0316) - [P0352 Ignition Coil "B" Primary/Secondary Circuit](https://diagxcar.com/codes/p0352) --- Source page: https://diagxcar.com/symptoms/car-shakes-at-idle Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.